A robust hysteresis current-controlled PWM inverter for linear PMSM drivenmagnetic suspended positioning system

Hysteresis current-controlled pulsewidth modulation (PWM) is very robust bu t it possesses nonconstant switching frequency, and it is difficult to use for high-performance position servo applications. This paper presents a rob ust hysteresis current-controlled PWM scheme for a magnetic suspended posit ioning system driven by an inverter-fed linear permanent-magnet synchronous motor having improved performance in these two areas. In the proposed cont rol scheme, the conventional hysteresis PWM mechanism is augmented by a rob ust harmonic spectrum-shaping controller. The error signal, which represent s the switching frequency deviated from the set one, is detected using a no tching filter inverse model. Then, the current command is adjusted by a rob ust compensation signal. The hysteresis band can be equivalently varied to let the dominant harmonic frequency of inverter output be constant, wherein the frequency can easily be changed by tuning the center frequency of the notch filter. The gating signal of switches is not needed to be sensed for making the proposed control. The constant-frequency control performance yie lded by the proposed controller is rather insensitive to the system disturb ances and the neutral voltage variation due to isolated Y connection. Throu gh applying the proposed PWM inverter, satisfactory position control requir ements can be achieved by properly setting the dominant harmonic frequency according to the electromechanical model of the positioning system.